"For years, PC programmers used x86 assembly to write performance-critical code. However, 32-bit PCs are being replaced with 64-bit ones, and the underlying assembly code has changed. This white paper is an introduction to x64 assembly. No prior knowledge of x86 code is needed, although it makes the transition easier."

I did get Dr Dobbs from time to time, but I also have the Michael Abrash book too (Zenn of code optimization, + graphic prog), a lot similar to the Inner Loops. I like the latter because I was only interested in certain types of asm code like JPEG DCT and well inner loops. Its always near by.

Ultimately I let the C compiler do the work of compiling C fragments that are 1 to 1 to asm opcodes, all inline. It just looks nicer than opting into the uglier asm syntax. I never learnt to use the mmx or sse stuff at all, I copped out.